import java.util.Scanner;

public class text2 {
    public static int fun2(int n){
        if(n==1)
            return 1;
        return n+fun2(n-1);
    }

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        System.out.println(fun2(n));
        sc.close();
    }
}
